Atypical Intraductal Proliferation (AIP) of the Prostate: Findings in Repeat Biopsy or Radical Prostatectomy in Patients who Met Pathologic Criteria for Active Surveillance.

The clinical significance of 'atypical intraductal proliferation' (AIP) is uncertain when found in prostate needle biopsy without intraductal carcinoma (IDC-P) or intermediate/high-grade prostate carcinoma (PCa). A retrospective review identified 168 patients diagnosed with AIP. Twenty-five (15%) were AIP alone, the rest with PCa. Follow-up biopsy or RP within 12 months was collected on patients with AIP-only, AIP and grade-group (GG)1, and AIP and GG2 PCa [<20% Gleason pattern 4 (GP4) without cribriform glands] who met pathologic criteria for active surveillance (AS). From 110 patients who met pathologic AS criteria, 66 did not have follow-up tissue. The findings among 28 patients with repeat biopsy were as follows: 14 (50%) were reclassified as a higher GG, including 3/6 (50%) from AIP-only [1 to GG1 and 2 to GG2 (60% and 20% GP4)], 8/16 from AIP/GG1 [50%, all to GG2 (1 with 30%, all others with <20% GP4)], 3/6 (50%) from AIP/GG2 (<20% GP4) [1 to GG3, and 2 to AIP/GG2 but with ≥20% GP4]. Five (18%) patients no longer met pathologic criteria for AS. Among patients with RP, 4 (33%) showed IDC-P. Quantitative and morphologic evaluation showed that higher number of cores, foci, and lumina in AIP with cribriform glands were more frequent in patients who were reclassified into higher grade-groups. In conclusion, AIP should be considered a potential marker for aggressive disease, warranting further evaluation. Although similar to IDC-P, it should remain a separate entity, as repeat biopsy does not show higher-than-expected AS exit rate.